The future availability of groundwater as a source of potable water is being jeopardized by the widespread occurrence of organic contaminants in groundwater supplies. A variety of pollutants have been detected, but none occur more frequently or at higher concentrations than trichloroethylene (TCE), a volatile organic compound (VOC) classified as a probable human carcinogen (Dyksen and Hess 1982). Remedial strategies now in widespread use for treating VOC-polluted groundwaters do not destroy contaminants during treatment, but instead merely shift the pollutants to another medium. For example, aeration produces contaminated air streams which are usually vented directly to the atmosphere, while activated carbon adsorption produces hazardous solid wastes. Efforts to manage polluted groundwater through well abandonment and blending contaminated water with clean water to meet standards are not viable long term options in a water limited environment, where all available resources must be utilized fully.
Heterogeneous photocatalysis shows promise as a chemical method that is capable of the complete, room temperature oxidation of volatile organic compounds such as TCE to environmentally innocuous species. In their pioneering work, Pruden and Ollis (1983) demonstrated the complete mineralization of dilute (10-50 ppm) aqueous solutions of TCE to carbon dioxide and hydrogen chloride by irradiating a 0.1 wt. % slurry of titanium dioxide with commercial black lights according to the following reaction: EQU Cl.sub.2 C.dbd.CClH+H.sub.2 O+3/2 O.sub.2 .fwdarw.2 CO.sub.2 +3 HCl
A key disadvantage to the aqueous phase photocatalytic process arises from the fact that the treated water is not suitable for human consumption because of the slurry of sub-micron sized titanium dioxide particles that remains after the reaction is complete. Indeed, the recovery of potable water from water treated by aqueous phase photocatalytic requires capital and energy intensive centrifugation or ultrafiltration.